In the medical field, implantable leads are used with a wide variety of medical devices. For example, implantable leads are commonly used to form part of implantable cardiac pacemakers that provide therapeutic stimulation to the heart by delivering pacing, cardioversion or defibrillation pulses. The pulses can be delivered to the heart via electrodes disposed on the leads, e.g., typically near distal ends of the leads. In that case, the leads may position the electrodes with respect to various cardiac locations so that the pacemaker can deliver pulses to the appropriate locations. Leads are also used for sensing purposes, or both sensing and stimulation purposes.
In addition, implantable leads are used in neurological devices such as deep-brain stimulation devices, and spinal cord stimulation devices. For example, leads may be stereotactically probed into the brain to position electrodes for deep brain stimulation. Leads are also used with a wide variety of other medical devices including, for example, devices that provide muscular stimulation therapy, devices that sense chemical conditions in a patient's blood, gastric system stimulators, implantable nerve stimulators, implantable lower colon stimulators, e.g., in graciloplasty applications, implantable drug or beneficial agent dispensers or pumps, implantable cardiac signal loops or other types of recorders or monitors, implantable gene therapy delivery devices, implantable incontinence prevention or monitoring devices, implantable insulin pumps or monitoring devices, and the like. In short, medical leads may be used for sensing purposes, stimulation purposes, drug delivery, and the like.
A number of challenges exist with respect to medical leads. In particular, new and improved lead designs are often needed to facilitate medical implantation to specific locations within a patient. For example, the stiffness characteristics of a medical lead may affect the ability to bend or conform a medical lead to a desired configuration. A stylet is often used to bend or form a distal region of the medical lead into a configuration that can allow for implantation of the lead tip into patient tissue at a desired location. As one example, J-shaped stylets may be inserted into a lumen of a medical lead to define a J-shaped configuration of a distal region of the medical lead once the distal region is inside a heart chamber. In that case, the distal tip of the lead may be implanted near the top of the right atrial chamber. Stiffness characteristics of the medical lead may affect the ability to achieve such a desired shape, however, and may also affect the shape of the medical lead following removal of the stylet.
Tissue fixation is another challenge relating to medical leads. In particular, a tip on the distal end of the medical lead may define certain shapes to improve fixation to tissue, and possibly harness the effects of fibrous tissue growth in order to anchor the lead tip in the tissue of a patient. For example, conventional leads commonly make use of distal tines to facilitate such anchoring in patient tissue. Distal tines, however, make lead removal much more traumatic to a patient because the tines can cause significant tissue damage upon removal from tissue. Moreover, the ability to adequately anchor a lead tip in tissue can also be complicated when the lead assumes different shapes, such as a J-shaped distal tip.